The main components of a waterjet propulsion apparatus are an intake section, a pump or pumping unit, and a nozzle. Fluid enters the unit through the intake section, which scoops water into the apparatus and directs it in the aft direction. The pump includes a rotor, also referred to as an impeller, and a stator located downstream thereof, both of which are located within a fluid conduit or flowpath. The rotor is turned on a stationary spindle and is driven by the prime mover of the vehicle. The rotor adds energy to the fluid, which accelerates the fluid to a higher velocity and pressure. The swirl induced by the rotor is for the most part removed by the stator, which does not rotate. At the outlet end of the conduit, downstream of the stator, is located a funnel-shaped nozzle, which reduces the cross-sectional area of the flowing stream, increases the velocity of the fluid and thereby generates thrust. In some embodiments the stator and the nozzle are an integrated unit. The thrust produced by the pump propels a marine vehicle.
The waterjet apparatus further includes within the rotor, a bearing cartridge including a bearing cavity having contained therein a bearing assembly. The bearing assembly may include back-to-back bearings, the most common being taper roller bearings. In conventional terrestrial vehicles, the taper roller bearings depend on external radial loads to generate a reaction preload between the bearings. This type of bearing system typically depends on a prescribed axial clearance to prevent the generation of a thermally induced axial load component thereby avoiding a thermal run away condition. A thermal run away condition exists where additional bearing heat generation results in yet a higher axial preload and higher heat generation. This cycle can continue until the bearings are destroyed.
Typically, in the design of the waterjet propulsion apparatus, the rotor system may not be heavy enough to generate a sufficient reaction preload between the bearings in a water mode. In an amphibious vehicle, the bearings also may need to endure 40 g+ shock loads while operating in a land mode. This condition makes it desirable to design a bearing support system to prevent relative motion between components during potentially high impact land mode operation and maintain or reduce that preload during normal water operation.
Accordingly, it is desirable to provide for an improved waterjet propulsion apparatus that includes a thermally insensitive solid bearing preload system for the bearing assembly. In addition, it is desirable to extend the wear life of the component elements of the bearing assembly by providing for little or no movement between the components. Finally, it is desired to provide a system for preventing damage to the bearing assembly within the bearing cavity in a waterjet propulsion apparatus that is less costly as compared to the alternative of replacing a damaged bearing assembly with a new one. The present invention addresses one or more of these needs.